1. Field of the Invention
The present invention relates to a three-dimensional measuring device.
2. Background Art
When an electronic component is mounted on a printed circuit board, a cream solder is generally first printed on a specific electrode pattern disposed on the printed circuit board. Adhesivity of this cream solder is then used to temporarily fix the electronic component on the printed circuit board. Thereafter, the above-described printed circuit board is conveyed to a reflow furnace, and soldering is performed by a routine reflow process. Recently, it has become necessary to perform an inspection of the printed state of the cream solder at a stage prior to conveyance to the reflow furnace, and three-dimensional measuring devices have been used for such inspection.
Various types of so-called non-contact type three-dimensional measuring devices using light have been proposed in recent years. Technology that relates, for example, to three-dimensional measuring devices utilizing the phase shift method has been proposed.
In a three-dimensional measuring device using this phase shift method, an irradiation means combining a light source and a sine wave pattern filter is used to illuminate a measurement object (such as a substrate or printed circuit board) using a light pattern having a sinusoidal (stripe shaped) light intensity distribution. Thereafter, points on the substrate are measured using an imaging means disposed directly above the substrate. A CCD camera having a lens and imaging elements may be used as the imaging means. In this case, intensity I of light at a point P on the image is given by the following equation:I=e+f×cos (φ)(within the formula, e=direct current optical noise (offset component), f=sine wave contrast (reflectivity), and φ=phase imparted by unevenness of the object).
At this time, the pattern light is moved so that the phase changes, for example, in 4 stages (e.g., φ+0, φ+π/2, φ+π, and φ+3π/2), images having intensity distributions corresponding to these phase shift changes (e.g., I0, I1, I2, and I3, respectively) are captured, and the modulation component α is determined based on the formula below.α=arctan {(I3−I1)/(I0−I2)}
This modulation component a can be used to determine the three-dimensional coordinates (X, Y, Z) at a measurement object point P on the measurement object (e.g., the cream solder), and these three-dimensional coordinates can be used to measure the three-dimensional shape of the measurement object and particularly to measure the height of the measurement object.
However, actual measurement objects include both tall measurement objects and short measurement objects. For example, in the case of cream solders, there are both thin film-shaped cream solders and protruding cream solders which forms a truncated cone shape. If the gaps between the lines of the irradiated light pattern are widened in order to adjust to the maximum height among such measurement objects, resolution ability becomes poor, and there is concern that measurement accuracy will worsen. On the other hand, although improving accuracy may be possible by narrowing the gaps between the lines, the height range capable of measurement would become insufficiently small, e.g., such narrow gaps would result in errors due differences in line orders.
Thus, for example, technology has been proposed for obtaining image data of higher resolution by performing the first imaging and then causing mutual displacement between the imaging element and the measurement object by one half pixel pitch of the imaging element before performing the second imaging (e.g., refer to Patent Citation 1).
Further, in order to solve the problem of the measurement-capable height range becoming too narrow, technology has also been proposed which combines a light pattern of a short period (line pitch) and a light pattern of a long period (e.g., refer to Patent Citation 2).